Variable inductor



- March 19; 1957 B. LlTMAN 2,786,186

VARIABLE INDUCTOR Original Filed June 14, 195] 2 Sheets-Sheet 2INVENTOR. BERNARD LITMAN gmmgw United States Patent VARIABLE INDUCTORBernard Litman, New York, N. Y., assignor to American Bosch ArrnaCorporation, a corporation of New York Original application June 14,1951, Serial No. 231,489,

now Patent No. 2,744,335, dated May 8, 1956. Divided and thisapplication February 18, 1953, Serial No. 337,561

2 Claims. (Cl. 336-119) The present invention relates to gravitypendulums and has particular reference to a pendulum sensitive to tiltsin only one plane and having self contained correction means tocompensate for acceleration forces other than gravity acting on thependulum.

This application is a division of application Serial Number 231,489,filed June 14, 1951, now Patent No. 2,744,335.

The present invention is particularly adapted for use on pendulumcontrolled gyroscopic devices installed on moving land, sea or air craftwhere the pendulums are subjected to acceleration forces other thangravity which ultimately cause inaccuracies in :the gyroscopicindication if not corrected. Copending application Serial Number738,242, filed March 29, 1947, by George Agins for InstrumentStabilization System for example, shows a stable element in whichacceleration forces other than gravity acting on the control pendulumsare neutralized by applying a counter torque to the pendulum pivot by atorque motor. The present invention is an improvement over the pendulumand torque motor combination there shown in which the pendulum and itscorrection device are united in a single unit where the correction motorarmature is also the weight for the pendulum.

In accordance with the present invention, a solenoid winding is attachedto the object whose .tilt from the vertical in a predetermined plane isto be detected, said solenoid winding having its longitudinal axis inthe tilt plane in a normally horizontal position and situated in theannular space between two mechanically coupled coaxial iron cylinderssuspended from the tilting object by light fiat flexible leaf springs ortapes. The leaf springs are attached to the cylinders in a manner whichallows axial displacement of the cylinders and yet resists motion of thecylinders in a direction perpendicular to the predetermined plane, i. e.the axis of the cylinders is perpendicular to the plane of the leafsprings.

As the object tilts out of the vertical through a small angle with acomponent tilt in a predetermined plane, the iron cylinders aredisplaced axially with respect to the solenoid and the magnitude of thedisplacement provides a measure of the component tilt, when gravityalone acts on the cylinders.

However, the cylinders may also be displaced by forces other thangravity, such as that resulting from a change in speed of the craft forexample, and hence the position of the cylinders does not indicate thetrue vertical without correction.

The solenoid winding is energized in a manner such as to apply aneutralizing force to the cylinders and thereby cause the pendulum toindicate the true vertical. The entire solenoid winding is energizedfrom a constant alternating voltage center tapped power supply, and asignal voltage proportional in magnitude to the computed error producingforce and of the same frequency as the power supply, is applied betweenthe solenoid winding center tap and the power supply center tap. Themagnetic field within the solenoid is stronger in one half of thesolenoid than in the other half and the force and direction of pull onthe iron cylinders are dependent, respectively, on the magnitude andphase of the signal voltage. The force of the magnetic attraction actingon the iron cylinder therefore neutralizes the external error producingforce applied to the pendulum causing the pendulum to indicate the truevertical.

The preferred embodiment to be described has numerous advantages overpreviously used methods and devices. It requires a minimum of space forinstallation and is simple to construct. Bearings and theirdisadvantages are eliminated by the use of flexible tapes instead ofrigid shafts in bearings. Other advantages will become evident in thedescription of the invention.

For a better understanding of the invention reference may be had to theaccompanying drawings, in which Fig. 1 is a cross sectional view of thependulum-linear force motor and its pickup device,

Fig. 2 is a pictorial representation of the unit shown in Fig. 1, and

Fig. 3 is a schematic wiring diagram showing the electrical connectionsto the unit of Fig. 1.

Turning now to Figs. 1 and 2, a cylinder 10 of nonmagnetic materialpreferably brass is secured to frame 11 by its extensions 12 which areformed by removing a portion of cylinder 10 leaving a vertical space 13between the extensions 12. The extensions 12 are fastened to frame 11 byscrews 14 passing through the flanges 12' of extensions 12. The outersurface of cylinder 10 is recessed to receive and hold the solenoidwinding 15.

The extended hub 16 of non-magnetic, preferably aluminum, end piece 17(shown partly broken away in Fig. 2) fits into the bore of iron cylinder18, While the iron cylinder 19, coaxial with cylinder 18 fits intorecess 20 in end piece 17. The iron cylinders 18 and 19 and end piece 17are then placed so that the cylinder 10 and solenoid 15 are situated inthe annular space between cylinders 18 and 19. The hub 21 ofnon-magnetic, preferably aluminum, end piece 22, is inserted intocylinder 18 while cylinder 19 fits into the recesses 23 of end piece 22.End piece 22 is shaped so that it fits loosely in the vertical space 13between extensions 12 of cylinder Ill. Non-magnetic bolt 24 is passedthrough end piece 17, cylinder 18 and end piece 22 and nut 25 istightened on bolt 24 to urge end pieces 17 and 22 together, therebyforcing the end pieces 17, 22 against the ends of cylinders 18, 19 inorder to hold the cylinders 18, 19 in a fixed relative position.Cylinders 18 and 19 are equal in length and are shorter than solenoid15.

The armature assembly, A, consisting of cylinders 18 and 19, end pieces17 and 22, bolt 24 and nut 25, is suspended out of contact with cylinder10 by the steel tapes 26 and is normally in a position where cylinders18, 19 are substantially coaxial with and longitudinally centered withrespect to solenoid 15. The upper ends of tapes 26 are fastened to frame11 by the bolts 29 and nuts 36. The lower ends of tapes 26 are clampedto support 31 by the rectangular pieces 32 and rivets 32' while supports31 are fastened to iron cylinder 19 by the screws 33. The rectangularpieces 28, 32 insure that the tapes 26 are tightly clamped at the edgesof block 27 and supports 31 so that the length of the tapes 26 does notvary.

Armature assembly A is free to swing through a limited longitudinaldisplacement, i. e. in the vertical plane containing the axis ofsolenoid 15. Motion perpendicular to this plane is restrained by thesteel tapes 26 which have the long dimension (of their cross section) atright angles to the axis of cylinder 19. However, when an excessiveforce, due to shock for example, is applied in the directionperpendicular to the longitudinal axis, the tapes 26 temporarily buckleand the cylinder 18 bears against the cylinder 10. When the excessiveforce is removed, however, the unit is again ready for operation withouthaving suffered any permanent injury.

In operation, the displacement of frame 11 from the vertical is not morethan a few degrees, as for example when secured to a stabilized gimbalring of a vertical spin axis gyro. A novel electrical pickup device B isinstalled between block 27 and iron cylinder 19 to detect thedisplacement of the pendulum weight, i. e. the armature assembly, A,from its zero position, which is the same as the displacement of frame11 from the vertical.

An iron cylinder 38 is secured to the block 27 by passing strap 39 underthe cylinder 38 and fastening strap 39 securely to block 27 with bolt 40and its associated nut (not shown), or by any other suitable method.

A non-magnetic circular collar 41 having a cross scction resembling theletter T with the horizontal bar of the T on the inner surface and thevertical bar of the T extending outwardly, ,is forced into the center ofcylinder 3S.

Solenoid winding =52 wound on a tubular magnetic core 42 is insertedinto the collar 41, and cup shaped end caps 43 and 44 are fitted overwinding 42 with the inner ends meeting the axially longer portion of thecollar 41. A bolt 45 is inserted through end cap 43, solenoid core 42',end cap 44, and nut 46 tightened on bolt 45, to force end caps 43 and 44into position against collar 41 and core 42'. Thus. the circuit for themagnetic flux developed when solenoid winding 42 is energized is fromcore 42 through end cap 43, annular air gap 47, cylinder 38, annular airgap 48, end cap 44 back to core 42', thereby producing a substantiallyradial magnetic flux in the air gaps 47 and 48.

Located in the air gaps 47 and 48 are the solenoids .9 and 50respectively wound on the non-magnetic shells 51 and 52. The shells 51and 52 are fastened to supports 31 by screws 53, for example, and aredisplaced longitudinally in the air gaps 47 and 48 whenever the armatureassembly A is longitudinally displaced with respect to block 27.

Solenoid winding 42 is energized by a constant alternating voltage (Fig.3) and a substantially radial constant alternating magnetic field isproduced in the air gaps 47 and 48 thereby. When pendulum assembly A iscentered in the zero position, i. e. where it indicates that frame 11 isvertical, an equal voltage is induced in each winding 49 and 50, whichare electrically connected in series opposition so that the voltageacross the two windings 49 and 50, and made available at terminals 34 iszero. When frame 11 tilts out of the vertical the pendulum assembly y Ais displaced from the zero position thereby displacing solenoids 49 and50 proportionally, so that the voltages induced in windings 4? and 59are no longer equal, and the magnitude of the voltage at terminals 34 isproportional to the displacement of pendulum A while the phase of thevoltage indicates the direction of displacement. The voltage atterminals 34 may be used to control a torque motor on the horizontalaxis of the gyro in the well known manner to cause erection of the gyrospin axis into the vertical.

To describe the operation of the invention, assume that the longitudinalaxis of the cylinders 13, 18, 19 is parallel to the longitudinal axis ofthe vessel carrying the pendulums, i. e. the pendulum is sensitive todisplacements in the pitch plane. In this case a change in the forwardspeed of the ship causes a force proportional to the rate of change offorward speed dSy/n't to be applied to the armature assembly A, causingthe assembly A to move axially resulting in an error in the indicationof the true vertical. (The assembly A moves axially until the componentof the gravitational force perpendicular to the plane of tapes 26tending to return the assembly A to the normal position balances theforce due to dSj/di tending to move the assembly A away from the zeroposition.)

Solenoid 15 is employed to apply a correcting force to assembly A ofsuch magnitude and direction that the forces due to accelerations otherthan gravity are neutralized thereby and the pendulum indicates the truevertical.

With reference to Fig. 3, solenoid 15 is energized from a center tappedconstant source of voltage, illustrated in Fig. 3 as transformer 55, theprimary winding 54 of which is energized from a constant alternatingvoltage supply, and the center-tapped secondary winding 56 of which isconnected across solenoid winding 15. Those skilled in the art willecognize that a source of direct voltage may be alternatively employedto energize solenoid 15, if desired.

It has been well established in electromagnetic theory that themagnitude of the force of pull on a magnetic core is constant when thecore penetrates between to 85 percent (approximately) into a solenoidand is proportional to the square of the magnitude of the magnetizingcurrent. Also the force of pull is zero when the core is substantiallycentered longitudinally Within the solenoid, since both halves of thesolenoid apply equal and opposite forces to the core.

Thus, when solenoid 15 is energized solely by the constant excitingvoltage 2V, from transformer 55 and cylinders 18 and 19 aresubstantially centered with respect to solenoid 15, the cores 18 and 19are subjected to equal and opposite forces, proportional in magnitude toV so that the assembly A assumes a position dependent only on theacceleration forces acting thereon.

Whenever the vessel undergoes a change in speed, a signal voltage E, ofthe same frequency as the exciting voltage and proportional in magnitudeto the calculated error producing force on assembly A, i. e.,proportional to is made available to terminals 59 (Fig. 3) from acircuit which is well known to those in the art and will not bedescribed here. Terminals 59 are connected to center tap 6% on thesolenoid winding 15 and to center tap 61 and secondary winding 56 sothat the current in one half of solenoid 15 is increased and isproportional to V+E, while the current in the other half of solenoid 15is decreased and is proportional to V-E, whence a stronger magneticfield exists in one half of solenoid 15 than in the other half. Thephase of the signal voltage at terminals 59 depends on whether thevessel is accelerating or decelerating and the phase relationshipbetween the signal and exciting voltages determines which half ofsolenoid 15 produces the stronger magnetic field. In operation the halfof solenoid 15 which is toward the forward part of the craft producesthe stronger magnetic field during acceleration of the craft while theother, or after half of solenoid 15 produces the stronger magnetic fieldduring deceleration of the craft. Thus when the forces due toacceleration tend to move the assembly A toward the rear of the craft,the forward half of solenoid 15 is the more strongly energized half andtends to draw the iron cylinders 18 and 19 forward with a forceproportional to (V-l-E) while the after half of solenoid 15 tends todraw iron cylinders 18 and 19 towards the rear with a force proportionalin magnitude to (VE) The total force on cylinders 18 and 19 isproportional to the difference between (V-l-E) and (Vl'5) or 4EV, whichis proportional to E since 4V is a constant. Since the direction of thisforce is forward the acceleration force due to the change in speed isneutralized so that the assembly A remains stationary and indicates thetrue vertical. Similarly, when the craft decelerates and the assembly Atends to move forward the rear half of solenoid 15, more stronglyenergized than the forward half, tends to draw the iron cylinders 13 and19 toward the rear with a force which neutralizes the deceleration forceso that the pendulum indicates the true vertical.

In a similar fashion computed corrections may be applied to the pitchpendulum to counteract the effects of skid, and to the roll pendulum tocounteract the effects of Coriolis acceleration, change in ships courseand the east west motion of own ship. The derivation of the computedcorrection voltages for these effects is contained in application SerialNumber 738,242 previously referred to.

From the foregoing it will be seen that I have provided means forobtaining all of the objects and advantages of the invention.

I claim:

1. In a device of the character described, a support, a magneticcylinder connected to said support, a first solenoid concentric andcoaxial with said magnetic cylinder and supported therein by amonmagnetic ring, a magnetic armature and magnetic end caps for saidsolenoid, annular air gaps between said end caps and the adjacentportions of said magnetic cylinder, and a pair of solenoidssubstantially coaxial with said first solenoid and said cylinder andmovable relative thereto simultaneously and to the same extent, saidpair of solenoids being located in said air gaps the output of saidsolenoids being connected in series whereby their difierence indicatesthe position of said solenoids with respect to said support.

2. In a device of the character described, a support,

a magnetic cylinder connected to said support, a first solenoidconcentric and coaxial with said magnetic cylinder and supported thereinby a nonmagnetic ring, a magnetic armature and magnetic end caps forsaid solenoid, annular air gaps between said end caps and the adjacentportions of said magnetic cylinder, and a pair of solenoidssubstantially coaxial with said first solenoid and said cylinder andmovable relative thereto simultaneously and to the same extent, one ofsaid pair of solenoids being located in the air gap between one of saidend caps and said cylinder and the other of said pair of solenoids beinglocated in the air gap between the other of said end caps and saidcylinder the output of said solenoids being connected in series wherebytheir diiierence indicates the position of said solenoids with respectto said support.

References Cited in the file of this patent UNITED STATES PATENTS2,452,862 Neil Nov. 2, 1948 2,586,010 Divoll Feb. 19, 1952 2,621,224Priest Dec. 9, 1952 2,627,062 Graham Ian. 27, 1953 FOREIGN PATENTS354,704 Germany June 15, 1922

